Branched polymers described by bond lattice animals will undergo a collapse transition if the fugacity for loops is increased. Based on analysis of extensive enumerations by Sykes and collaborators of cubic-lattices embeddings, we conclude that the specific heat diverges if the tricritical point is approached, keeping the number of occupied sites constant, but exhibits a cusp if the number of bonds is fixed. This behavior is explained in terms of a ‘‘Fisher renormalization.’’

• Received 19 April 1988

DOI:https://doi.org/10.1103/PhysRevB.38.6736